In the process for production of semiconductor devices including flat panel displays such as TFT liquid crystal devices as well as microprocessors, memories and CCD, patterns or a thin film in the order of sub-microns or quarter-microns are formed on the surface of a substrate made of silicon, silicon oxide (SiO2), glass or the like. Therefore, in the respective steps of such a production process, it is extremely important to highly clean the surface of the substrate by removing even a trace amount of contaminants therefrom. Among these contaminants, in particular, fine contaminants such as particle contaminants and metal contaminants are difficult to remove completely. However, since such contaminants tend to cause deterioration in electric properties and yield of the semiconductor devices, it is necessary to possibly remove the contaminants from the surface of the substrate prior to transferring the substrate to subsequent processes. In general, these contaminants are removed by cleaning the surface of the substrate using a cleaning solution.
In recent years, in the production of semiconductor devices, it is required to further enhance a throughput and a production efficiency thereof. In the substrate used for production of the semiconductor devices, which tend to be more and more reduced in size and highly integrated, it has been demanded to provide a cleaning solution and a cleaning method which are capable of not only removing particle contaminants and metal contaminants from the surface of the substrate, but also allowing the thus cleaned substrate to exhibit an excellent readhesion-preventing property after removal of these contaminants, thereby rapidly and highly cleaning the surface of the substrate.
In general, it is known that an aqueous alkali solution is useful as the cleaning solution for removing the particle contaminants. For the purpose of cleaning the surface of a substrate for semiconductor devices, there have been used aqueous alkali solutions such as an aqueous ammonia solution, an aqueous potassium hydroxide solution and an aqueous tetramethylammonium hydroxide solution. Further, there has been widely used a cleaning method (“SC-1 cleaning” or “APM cleaning”) using a cleaning solution containing ammonia, hydrogen peroxide and water (also called “SC-1 cleaning solution” or “APM cleaning solution”) (W. Kern and D. A. Puotinen “RCA Review”, p. 187, June (1970)).
In addition, recently, in order to improve properties of such alkali cleaning solutions, specifically, in order to prevent the surface of the substrate for semiconductor devices from being etched and roughened, enhance a wettability of the surface of the substrate therewith, and improve a cleanability for removal of particle contaminants therefrom, there have been proposed various methods in which various surfactants are added to the alkali cleaning solutions.
For example, in order to prevent the surface of the substrate from being roughened by the cleaning solution, there has been proposed the method of adding a surfactant to an alkaline aqueous hydrogen peroxide solution to control a contact angle of the cleaning solution with the surface of the substrate to not more than 10° (Japanese Patent Application Laid-open (KOKAI) No. 5-335294 (1993)). In addition, in order to improve a wettability of the surface of the substrate with the cleaning solution, there has been proposed the hydrogen peroxide-containing alkali cleaning solution prepared by adding an ethyleneoxide-added nonionic surfactant in which the number of moles of ethyleneoxide added is 3 to 10 (Japanese Patent No. 3169024).
Further, in order to prevent the surface of a silicon substrate as a typical substrate for semiconductor devices from being etched, there has been proposed the method of adding various surfactants to an alkali cleaning solution (Japanese Patent Application Laid-open (KOKAI) No. 2001-40389). In particular, in order to improve a cleanability for removal of organic contaminants, there has been proposed the cleaning solution containing a specific surfactant which is used to clean the surface of the substrate for semiconductor devices (Japanese Patent Application Laid-open (KOKAI) No. 11-121418 (1999)). In order to improve a cleanability for removal of contaminants, there has also been proposed the method of adding alkylbenzenesulfonic acid to the hydrogen-peroxide-containing alkali cleaning solution (Japanese Patent Application Laid-open (KOKAI) No. 7-245281 (1995)). Further, in order to improve a cleanability for removal of particle contaminants, there has been proposed the method of adding a fluorine-based surfactant composed of a fluoroalkylsulfoneamide compound to an APM cleaning solution (Japanese Patent Application Laid-open (KOKAI) No. 5-251416 (1993)).
Further, in addition to the above alkali cleaning solution, an acid cleaning solution is also useful for cleaning the substrate for semiconductor devices. In general, the acid cleaning solution is effective to remove metal contaminants from the surface of the substrate, but is unsuitable for removing particle contaminants therefrom. For this reason, there have also been proposed the methods of adding various surfactants to the acid cleaning solution in order to improve a cleanability for removal of the particle contaminants, etc. For example, there has been proposed the method of cleaning a silicon wafer using a specific surfactant and hydrofluoric acid (Japanese Patent Application Laid-open (KOKAI) No. 7-216392 (1995)).
Further, there has been proposed the method of adding a surfactant and ozone to an aqueous hydrofluoric acid solution used for cleaning a silicon wafer (Japanese Patent Application Laid-open (KOKAI) No. 8-69990 (1996)). In addition, there has been proposed the method of adding an organic acid compound to a dispersant and/or surfactant in order to remove metal impurities and particle contaminants adsorbed onto the substrate provided on the surface thereof with a metal wiring (Japanese Patent Application Laid-open (KOKAI) No. 2001-7071).
In recent years, with the tendencies toward further reduction in size and highly-laminated structure of semiconductor devices, new metal materials such as copper (Cu) and tungsten (W) have been increasingly used as materials for a metal wiring connecting between fine semiconductor devices (hereinafter referred to merely as “wiring”) or an electrode in the semiconductor devices (hereinafter referred to merely as “electrode”). More specifically, for example, as the wiring material, conventional aluminum (Al) has been recently replaced with copper (Cu) having a lower resistivity than that of Al.
Further, other new materials are also used for formation of inter layer dielectrics disposed between semiconductor devices having a laminated structure. As to the inter layer dielectrics, conventional SiO2 films tend to be replaced with low dielectric films made of organic polymer materials or inorganic polymer materials having a lower dielectric than that of SiO2. The inter layer dielectric is exposed to the surface of the substrate together with a metal wiring upon a cleaning step conducted after forming the metal wiring on the surface of the substrate (hereinafter occasionally referred to as “back end process”) during the production process of the semiconductor devices.
Further, tungsten which has a low resistivity and is advantageous for fine processing, has been recently used as an electrode material. The electrode is usually exposed to the surface of the substrate upon a cleaning step conducted before forming the metal wiring thereon (hereinafter occasionally referred to as “front end process”). Conventionally, since the surface of the substrate to be cleaned in the front end process is wholly composed of a Si compound, even a trace amount of contaminants adhered thereonto adversely affect the resultant semiconductor devices. Therefore, it is necessary to highly clean the surface of the substrate, thereby essentially requiring a strong cleaning of the substrate by RCA cleaning method.
Further, in recent years, it has also been attempted to apply various proposals mentioned above to substrates using the above new materials that are exposed to the surface thereof, in order to highly clean the surface of the substrates.
The conventional back end process for cleaning the substrates having an Al wiring has been simply conducted using ultrapure water or an organic solvent since the Al wiring tends to be readily damaged by a strong acid or a strong alkali, and adverse influence thereon by metal contaminants in the back end process is lower than that in the front end process. However, when Cu is used instead of Al, there arise the following two additional problems.
First, since Cu is one of metal contaminants most unfavorable for Si, there arises such a problem that a diffusion velocity of Cu into an oxide film (SiO2) formed on the surface of the semiconductor device is high, thereby causing much severer influences thereon as compared to those by Al.
Secondary, there is such a problem that Cu is incapable of dry-etching unlike Al. In order to produce a Cu wiring, it is inevitably required to use a method of previously forming a groove for the Cu wiring on an insulating film, subjecting the insulating film to copper-plating and then removing unnecessary portions of the copper-plated layer by CMP (Chemical Mechanical Polishing) method, i.e., a so-called Damasin method, or the like.
Upon forming the wiring by the above Damasin method, there arises such a problem that the Cu wiring or the low dielectric film were contaminated with a large amount of Cu used and abrasive particles (particles such as typically aluminum oxide particles) contained in a slurry used upon the CMP. Such contaminants on the surface of the substrate are no longer removed only by the simple cleaning method using ultrapure water or an organic solvent, thereby causing significant problems.
When the conventional RCA cleaning method using a strong acid or a strong alkali is used to remove the above contaminants, there arises such an additional problem that the new metal materials such as Cu and W are dissolved in hydrogen peroxide. In addition, the hydrophobic surface of the low dielectric film exhibits a poor wettability with the cleaning solution and, therefore, tends to repel the cleaning solution. As a result, in particular, it may be difficult to completely remove particle contaminants from the surface of the low dielectric film.
Accordingly, in the cleaning process for cleaning the substrate having the above new materials on the surface thereof, there will arise such a significant problem that the RCA cleaning solution containing hydrogen peroxide is no longer usable. For this reason, it has been strongly demanded to develop a new cleaning solution capable of cleaning the substrate whose surface contains the new metal materials that tend to be damaged by chemicals such as hydrogen peroxide.
To solve these problems, there have been developed the cleaning solutions containing various surfactants as described above. However, the conventional cleaning solutions have failed to exhibit a good cleanability for removing metal contaminants or particle contaminants, and sufficiently prevent re-adhesion of the contaminants removed, and further satisfy the following requirements (1) to (3), thereby causing problems upon cleaning the surface of the substrate.
(1) To be free from precipitation and white turbidity of the surfactant in the form of oil droplets in the cleaning solution at room temperature or upon heating, as well as deterioration in cleanability and residual oil droplets on the surface of the substrate;
(2) To have a low foaming property and show no adverse influences on the operation of a cleaning apparatus; and
(3) Surfactant is made of materials that have no adverse influences on natural environment, and the waste cleaning solution is capable of being appropriately treated.
For example, since anionic surfactants usually have no cloud point, the cleaning solution containing such anionic surfactants can be used under a high temperature condition (e.g., not less than 80° C.), whereby a high-cleaning effect can be expected. However, since the anionic surfactants have a high foaming property, the use of a cleaning solution containing such anionic surfactants tends to adversely affect the operation of the cleaning apparatus.
Also, nonionic surfactants have a high cleanability and a low foaming property, but usually show a low cloud point. Therefore, when the cleaning solution containing such nonionic surfactants are used at a high temperature to attain a high-cleaning effect, the surfactants are coagulated in the form of oil droplets in the cleaning solution, thereby causing such a problem that residual oil droplets adhered onto the substrate are present after cleaning.